Synthetic hydrocarbons have been used as lubricant components for automotive, aviation, and industrial applications. Poly-α-olefins (PAOs, polyalphaolefins) are synthetic hydrocarbons that have been used as lubricant base oils. PAOs exhibit desirable flow properties at low temperatures, high thermal and oxidative stability, low evaporation losses at high temperatures, high viscosity index, good friction behavior, good hydrolytic stability, and good erosion resistance. PAOs are relatively nontoxic and are miscible with a variety of conventional base stocks, including mineral oils, Group I-III and Group III+ oils, GTL fluids and esters. Consequently, PAOs are suitable for use in engine oils, compressor oils, hydraulic oils, gear oils, and greases.
PAOs have been commercially manufactured by catalytic oligomerization of olefins. The manufacturing process generates a distillate byproduct that contains mostly light C8H16 to C30H60 oligomers (averaging C20H40 or less) exhibiting a relatively low average molecular weight of about 280 or less. The distillate byproducts are usually recycled to produce more PAO product. The distillate byproduct typically has a significant incidence of long chain branching and highly substituted double bonds (tri- or tetra-substituted olefins). Highly substituted olefins usually exhibit lower reactivity than less substituted olefins. Recycle of highly substituted olefins and/or olefins with long chain branching can negatively impact physical properties of the final lube product, such as viscosity index (VI), volatility, and thermal-oxidative stability.
Lubricants have been identified as a critical feature for future lubricants in automotive applications for the future. To provide enhanced fuel economy while maintaining or improving other performance features for lubricants, base stocks that exhibit lower friction coefficients are needed.
For automotive engine lubricant formulations, it is generally preferred to have lower viscosity fluids, e.g., below 10 cSt. Lower viscosity is known to impart lower viscous drag thus offering better energy efficiency or fuel economy. Both low viscosity and high viscosity fluids are useful in industrial lubricant formulations to yield different ISO vis grad lubricants. For industrial lubricant formulations, it is generally important to use fluids of high Viscosity Index (VI) and high hydrolytic stability.
For both engine and industrial lubricant applications, it is important to have a lubricant formulation with a low friction coefficient. Fluids with low friction coefficients exhibit low frictional loss during lubrication. Low frictional loss is critical for improved energy or fuel efficiency of formulated lubricants.
Friction coefficients can be measured by a High Frequency Reciprocating Rig (HFRR) test. The test equipment and procedure are similar to the ASTM D6079 method except the test oil temperature is raised from 32° C. to 195° C. at 2° C./minute, 400 g load, 60 Hz frequency, and 0.5 mm stroke length or 400 g load, 60 Hz frequency at constant temperature, such as 100° C. or 60° C. The test can measure average friction coefficient and wear volume.
It would be desirable to have a process for making polar PAOs in which distillate byproducts could be processed and converted to polar PAOs. It would further be desirable to have a process for making polar PAOs in which recycle of distillate byproduct could be avoided. It would be further yet desirable to have a base stock that exhibits a low coefficient of friction.